Rendering for computer-mediated reality systems

ABSTRACT

In general, techniques are described for adapting higher order ambisonic audio data to include three degrees of freedom plus effects. An example device configured to perform the techniques includes a memory, and a processor coupled to the memory. The memory may be configured to store higher order ambisonic audio data representative of a soundfield. The processor may be configured to obtain a translational distance representative of a translational head movement of a user interfacing with the device. The processor may further be configured to adapt, based on the translational distance, higher order ambisonic audio data to provide three degrees of freedom plus effects that adapt the soundfield to account for the translational head movement, and generate speaker feeds based on the adapted higher order ambient audio data.

TECHNICAL FIELD

This disclosure relates to processing of media data, such as audio data.

BACKGROUND

A higher-order ambisonics (HOA) signal (often represented by a plurality of spherical harmonic coefficients (SHC) or other hierarchical elements) is a three-dimensional representation of a soundfield. The HOA or SHC representation may represent the soundfield in a manner that is independent of the local speaker geometry used to playback a multi-channel audio signal rendered from the SHC signal. The SHC signal may also facilitate backwards compatibility as the SHC signal may be rendered to well-known and highly adopted multi-channel formats, such as a 5.1 audio channel format or a 7.1 audio channel format. The SHC representation may therefore enable a better representation of a soundfield that also accommodates backward compatibility.

SUMMARY

This disclosure relates generally to auditory aspects of the user experience of computer-mediated reality systems, including virtual reality (VR), mixed reality (MR), augmented reality (AR), computer vision, and graphics systems. The techniques may enable rendering of higher-order ambisonic (HOA) audio data for VR, MR, AR, etc. that accounts for three degrees freedom (yaw, pitch, and roll) in terms of head movements and limited translational movements of the head, which is a form of audio rendering referred to as three degrees of freedom plus (3DOF+) audio rendering.

In one example, the techniques are directed to a device comprising a memory configured to store higher order ambisonic audio data representative of a soundfield, and a processor coupled to the memory, and configured to obtain a translational distance representative of a translational head movement of a user interfacing with the device. The processor may further be configured to adapt, based on the translational distance, higher order ambisonic audio data to provide three degrees of freedom plus effects that adapt the soundfield to account for the translational head movement, and generate speaker feeds based on the adapted higher order ambient audio data.

In another example, the techniques are directed to a method comprising obtaining a translational distance representative of a translational head movement of a user interfacing with the device. The method may further comprise adapting, based on the translational distance, higher order ambisonic audio data to provide three degrees of freedom plus effects that adapt a soundfield represented by the higher order ambisonic audio data to account for the translational head movement, and generating speaker feeds based on the adapted higher order ambient audio data.

In another example, the techniques are directed to a device comprising means for obtaining a translational distance representative of a translational head movement of a user interfacing with the device. The device may further comprise means for adapting, based on the translational distance, higher order ambisonic audio data to provide three degrees of freedom plus effects that adapt a soundfield represented by the higher order ambisonic audio data to account for the translational head movement, and means for generating speaker feeds based on the adapted higher order ambient audio data.

In another example, the techniques are directed to a non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to obtain a translational distance representative of a translational head movement of a user interfacing with the device, adapt, based on the translational distance, higher order ambisonic audio data to provide three degrees of freedom plus effects that adapt a soundfield represented by the higher order ambisonic audio data to account for the translational head movement, and generate speaker feeds based on the adapted higher order ambient audio data.

The details of one or more examples of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of various aspects of the techniques will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating spherical harmonic basis functions of various orders and sub-orders.

FIGS. 2A and 2B are diagrams illustrating systems that may perform various aspects of the techniques described in this disclosure.

FIG. 3 is a diagram illustrating an example of a VR device worn by a user.

FIG. 4 is a block diagram illustrating in more detail the audio playback system shown in FIGS. 2A and 2B in performing various aspects of the effect techniques described in this disclosure.

FIG. 5 is a diagram illustration in more detail how the effects unit shown in the example of FIG. 4 obtains the effects matrix in accordance with various aspects of the techniques described in this disclosure.

FIG. 6 is a diagram illustrating the depth map shown in FIG. 4 having been updated to reflect the mapping of the anchor points to the depth map in accordance with various aspects of the techniques described in this disclosure.

FIG. 7 is a diagram illustrating an example of a wearable device that may operate in accordance with various aspect of the techniques described in this disclosure.

FIGS. 8A and 8B are diagrams illustrating other example systems that may perform various aspects of the techniques described in this disclosure.

FIG. 9 is a flowchart illustrating an example process that the audio playback device may perform in accordance with various aspects of this disclosure.

DETAILED DESCRIPTION

There are various ‘surround-sound’ channel-based formats in the market. They range, for example, from the 5.1 home theatre system (which has been the most successful in terms of making inroads into living rooms beyond stereo) to the 22.2 system developed by NHK (Nippon Hoso Kyokai or Japan Broadcasting Corporation). Content creators (e.g., Hollywood studios) would like to produce the soundtrack for a movie once, and not spend effort to remix it for each speaker configuration. A Moving Pictures Expert Group (MPEG) has released a standard allowing for soundfields to be represented using a hierarchical set of elements (e.g., Higher-Order Ambisonic—HOA—coefficients) that can be rendered to speaker feeds for most speaker configurations, including 5.1 and 22.2 configuration whether in location defined by various standards or in non-uniform locations.

MPEG released the standard as MPEG-H 3D Audio standard, formally entitled “Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 3: 3D audio,” set forth by ISO/IEC JTC 1/SC 29, with document identifier ISO/IEC DIS 23008-3, and dated Jul. 25, 2014. MPEG also released a second edition of the 3D Audio standard, entitled “Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 3: 3D audio, set forth by ISO/IEC JTC 1/SC 29, with document identifier ISO/IEC 23008-3:201x(E), and dated Oct. 12, 2016. Reference to the “3D Audio standard” in this disclosure may refer to one or both of the above standards.

As noted above, one example of a hierarchical set of elements is a set of spherical harmonic coefficients (SHC). The following expression demonstrates a description or representation of a soundfield using SHC:

${{p_{i}\left( {t,r_{r},\theta_{r},\varphi_{r}} \right)} = {\sum\limits_{\omega = 0}^{\infty}\;{\left\lbrack {4\pi{\sum\limits_{n = 0}^{\infty}\;{{j_{n}\left( {kr}_{r} \right)}{\sum\limits_{m = {- n}}^{n}\;{{A_{n}^{m}(k)}{Y_{n}^{m}\left( {\theta_{r},\varphi_{r}} \right)}}}}}} \right\rbrack e^{j\;\omega\; t}}}},$

The expression shows that the pressure p_(i) at any point {r_(r), θ_(r), φ_(r)} of the soundfield, at time t, can be represented uniquely by the SHC, A_(n) ^(m)(k). Here,

${k = \frac{\omega}{c}},$ c is the speed of sound (˜343 m/s), {r_(r), θ_(r), φ_(r)} is a point of reference (or observation point), j_(n)(·) is the spherical Bessel function of order n, and Y_(n) ^(m)(θ_(r), φ_(r)) are the spherical harmonic basis functions (which may also be referred to as a spherical basis function) of order n and suborder m. It can be recognized that the term in square brackets is a frequency-domain representation of the signal (i.e., S(ω, r_(r), θ_(r), φ_(r))) which can be approximated by various time-frequency transformations, such as the discrete Fourier transform (DFT), the discrete cosine transform (DCT), or a wavelet transform. Other examples of hierarchical sets include sets of wavelet transform coefficients and other sets of coefficients of multiresolution basis functions.

FIG. 1 is a diagram illustrating spherical harmonic basis functions from the zero order (n=0) to the fourth order (n=4). As can be seen, for each order, there is an expansion of suborders m which are shown but not explicitly noted in the example of FIG. 1 for ease of illustration purposes.

The SHC A_(n) ^(m)(k) can either be physically acquired (e.g., recorded) by various microphone array configurations or, alternatively, they can be derived from channel-based or object-based descriptions of the soundfield. The SHC (which also may be referred to as higher order ambisonic—HOA—coefficients) represent scene-based audio, where the SHC may be input to an audio encoder to obtain encoded SHC that may promote more efficient transmission or storage. For example, a fourth-order representation involving (1+4)² (25, and hence fourth order) coefficients may be used.

As noted above, the SHC may be derived from a microphone recording using a microphone array. Various examples of how SHC may be derived from microphone arrays are described in Poletti, M., “Three-Dimensional Surround Sound Systems Based on Spherical Harmonics,” J. Audio Eng. Soc., Vol. 53, No. 11, 2005 November, pp. 1004-1025.

To illustrate how the SHCs may be derived from an object-based description, consider the following equation. The coefficients A_(n) ^(m)(k) for the soundfield corresponding to an individual audio object may be expressed as: A _(n) ^(m)(k)=g(ω)(−4πik)h _(n) ⁽²⁾(kr _(s))Y _(n) ^(m*)(θ_(s),φ_(s)), where i is √{square root over (−1)}, h_(n) ⁽²⁾(·) is the spherical Hankel function (of the second kind) of order n, and {r_(s), θ_(s), φ_(s)} is the location of the object. Knowing the object source energy g(ω) as a function of frequency (e.g., using time-frequency analysis techniques, such as performing a fast Fourier transform on the PCM stream) allows us to convert each PCM object and the corresponding location into the SHC A_(n) ^(m)(k). Further, it can be shown (since the above is a linear and orthogonal decomposition) that the A_(n) ^(m)(k) coefficients for each object are additive. In this manner, a number of PCM objects can be represented by the A_(n) ^(m)(k) coefficients (e.g., as a sum of the coefficient vectors for the individual objects). Essentially, the coefficients contain information about the soundfield (the pressure as a function of 3D coordinates), and the above represents the transformation from individual objects to a representation of the overall soundfield, in the vicinity of the observation point {r_(r), θ_(r), φ_(r)}. The remaining figures are described below in the context of SHC-based audio coding.

FIGS. 2A and 2B are diagrams illustrating systems that may perform various aspects of the techniques described in this disclosure. As shown in the example of FIG. 2A, system 10 includes a source device 12 and a content consumer device 14. While described in the context of the source device 12 and the content consumer device 14, the techniques may be implemented in any context in which any hierarchical representation of a soundfield is encoded to form a bitstream representative of the audio data. Moreover, the source device 12 may represent any form of computing device capable of generating hierarchical representation of a soundfield, and is generally described herein in the context of being a VR content creator device. Likewise, the content consumer device 14 may represent any form of computing device capable of implementing the soundfield representation selection techniques described in this disclosure as well as audio playback, and is generally described herein in the context of being a VR client device.

The source device 12 may be operated by an entertainment company or other entity that may generate multi-channel audio content for consumption by operators of content consumer devices, such as the content consumer device 14. In many VR scenarios, the source device 12 generates audio content in conjunction with video content. The source device 12 includes a content capture device 300 and a content capture assistant device 302. The content capture device 300 may be configured to interface or otherwise communicate with a microphone 5. The microphone 5 may represent an Eigenmike® or other type of 3D audio microphone capable of capturing and representing the soundfield as HOA coefficients 11.

The content capture device 300 may, in some examples, include an integrated microphone 5 that is integrated into the housing of the content capture device 300. The content capture device 300 may interface wirelessly or via a wired connection with the microphone 5. Rather than capture, or in conjunction with capturing, audio data via microphone 5, the content capture device 300 may process the HOA coefficients 11 after the HOA coefficients 11 are input via some type of removable storage, wirelessly and/or via wired input processes. As such, various combinations of the content capture device 300 and the microphone 5 are possible in accordance with this disclosure.

The content capture device 300 may also be configured to interface or otherwise communicate with the soundfield representation generator 302. The soundfield representation generator 302 may include any type of hardware device capable of interfacing with the content capture device 300. The soundfield representation generator 302 may the use HOA coefficients 11 provided by the content capture device 300 to generate various representations of the same soundfield represented by the HOA coefficients 11. For instance, to generate the different representations of the soundfield using the HOA coefficients 11, soundfield representation generator 302 may use a coding scheme for ambisonic representations of a soundfield, referred to as Mixed Order Ambisonics (MOA) as discussed in more detail in U.S. application Ser. No. 15/672,058, entitled “MIXED-ORDER AMBISONICS (MOA) AUDIO DATA FO COMPUTER-MEDIATED REALITY SYSTEMS,” and filed Aug. 8, 2017.

To generate a particular MOA representation of the soundfield, the soundfield representation generator 302 may generate a partial subset of the full set of HOA coefficients 11. For instance, each MOA representation generated by the soundfield representation generator 302 may provide precision with respect to some areas of the soundfield, but less precision in other areas. In one example, an MOA representation of the soundfield may include eight (8) uncompressed HOA coefficients of the HOA coefficients 11, while the third order HOA representation of the same soundfield may include sixteen (16) uncompressed HOA coefficients of the HOA coefficients 11. As such, each MOA representation of the soundfield that is generated as a partial subset of the HOA coefficients 11 may be less storage-intensive and less bandwidth intensive (if and when transmitted as part of the bitstream 21 over the illustrated transmission channel) than the corresponding third order HOA representation of the same soundfield generated from the HOA coefficients 11.

Although described with respect to MOA representations, the techniques of this disclosure may also be performed with respect to full-order ambisonic (FOA) representations in which all of the HOA coefficients for a given order N are used to represent the soundfield. In other words, rather than represent the soundfield using a partial, non-zero subset of the HOA coefficients 11, the soundfield representation generator 302 may represent the soundfield using all of the HOA coefficients 11 for a given order N, resulting in a total of HOA coefficients equaling (N+1)².

In this respect, the higher order ambisonic audio data 11 may include higher order ambisonic coefficients 11 associated with spherical basis functions having an order of one or less (which may be referred to as “1^(st) order ambisonic audio data 11”), higher order ambisonic coefficients associated with spherical basis functions having a mixed order and suborder (which may be referred to as the “MOA representation” discussed above), or higher order ambisonic coefficients associated with spherical basis functions having an order greater than one (which is referred to above as the “FOA representation”).

The content capture device 300 may, in some examples, be configured to wirelessly communicate with the soundfield representation generator 302. In some examples, the content capture device 300 may communicate, via one or both of a wireless connection or a wired connection, with the soundfield representation generator 302. Via the connection between the content capture device 300 and the soundfield representation generator 302, the content capture device 300 may provide content in various forms of content, which, for purposes of discussion, are described herein as being portions of the HOA coefficients 11.

In some examples, the content capture device 300 may leverage various aspects of the soundfield representation generator 302 (in terms of hardware or software capabilities of the soundfield representation generator 302). For example, the soundfield representation generator 302 may include dedicated hardware configured to (or specialized software that when executed causes one or more processors to) perform psychoacoustic audio encoding (such as a unified speech and audio coder denoted as “USAC” set forth by the Motion Picture Experts Group (MPEG) or the MPEG-H 3D audio coding standard). The content capture device 300 may not include the psychoacoustic audio encoder dedicated hardware or specialized software and instead provide audio aspects of the content 301 in a non-psychoacoustic-audio-coded form. The soundfield representation generator 302 may assist in the capture of content 301 by, at least in part, performing psychoacoustic audio encoding with respect to the audio aspects of the content 301.

The soundfield representation generator 302 may also assist in content capture and transmission by generating one or more bitstreams 21 based, at least in part, on the audio content (e.g., MOA representations and/or third order HOA representations) generated from the HOA coefficients 11. The bitstream 21 may represent a compressed version of the HOA coefficients 11 (and/or the partial subsets thereof used to form MOA representations of the soundfield) and any other different types of the content 301 (such as a compressed version of spherical video data, image data, or text data).

The soundfield representation generator 302 may generate the bitstream 21 for transmission, as one example, across a transmission channel, which may be a wired or wireless channel, a data storage device, or the like. The bitstream 21 may represent an encoded version of the HOA coefficients 11 (and/or the partial subsets thereof used to form MOA representations of the soundfield) and may include a primary bitstream and another side bitstream, which may be referred to as side channel information. In some instances, the bitstream 21 representing the compressed version of the HOA coefficients may conform to bitstreams produced in accordance with the MPEG-H 3D audio coding standard.

The content consumer device 14 may be operated by an individual, and may represent a VR client device. Although described with respect to a VR client device, content consumer device 14 may represent other types of devices, such as an augmented reality (AR) client device, a mixed reality (MR) client device, a standard computer, a headset, headphones, or any other device capable of tracking head movements and/or general translational movements of the individual operating the client consumer device 14. As shown in the example of FIG. 2A, the content consumer device 14 includes an audio playback system 16, which may refer to any form of audio playback system capable of rendering SHC (whether in form of third order HOA representations and/or MOA representations) for playback as multi-channel audio content.

While shown in FIG. 2A as being directly transmitted to the content consumer device 14, the source device 12 may output the bitstream 21 to an intermediate device positioned between the source device 12 and the content consumer device 14. The intermediate device may store the bitstream 21 for later delivery to the content consumer device 14, which may request the bitstream. The intermediate device may comprise a file server, a web server, a desktop computer, a laptop computer, a tablet computer, a mobile phone, a smart phone, or any other device capable of storing the bitstream 21 for later retrieval by an audio decoder. The intermediate device may reside in a content delivery network capable of streaming the bitstream 21 (and possibly in conjunction with transmitting a corresponding video data bitstream) to subscribers, such as the content consumer device 14, requesting the bitstream 21.

Alternatively, the source device 12 may store the bitstream 21 to a storage medium, such as a compact disc, a digital video disc, a high definition video disc or other storage media, most of which are capable of being read by a computer and therefore may be referred to as computer-readable storage media or non-transitory computer-readable storage media. In this context, the transmission channel may refer to the channels by which content stored to the mediums are transmitted (and may include retail stores and other store-based delivery mechanism). In any event, the techniques of this disclosure should not therefore be limited in this respect to the example of FIG. 2A.

As noted above, the content consumer device 14 includes the audio playback system 16. The audio playback system 16 may represent any system capable of playing back multi-channel audio data. The audio playback system 16 may include a number of different renderers 22. The renderers 22 may each provide for a different form of rendering, where the different forms of rendering may include one or more of the various ways of performing vector-base amplitude panning (VBAP), and/or one or more of the various ways of performing soundfield synthesis. As used herein, “A and/or B” means “A or B”, or both “A and B”.

The audio playback system 16 may further include an audio decoding device 24. The audio decoding device 24 may represent a device configured to decode bitstream 21 to output HOA audio data 15 (which may form the full third order HOA representation or a subset thereof that forms an MOA representation of the same soundfield or decompositions thereof, such as the predominant audio signal, ambient HOA coefficients, and the vector based signal described in the MPEG-H 3D Audio Coding Standard). As such, the HOA audio data 15 may be similar to a full set or a partial subset of the HOA coefficients 11, but may differ due to lossy operations (e.g., quantization) and/or transmission via the transmission channel. The audio playback system 16 may, after decoding the bitstream 21 to obtain the HOA audio data 15, render the HOA audio data 15 to output speaker feeds 25. The speaker feeds 25 may drive one or more speakers (which are not shown in the example of FIG. 2A for ease of illustration purposes). Ambisonic representations of a soundfield may be normalized in a number of ways, including N3D, SN3D, FuMa, N2D, or SN2D.

To select the appropriate renderer or, in some instances, generate an appropriate renderer, the audio playback system 16 may obtain loudspeaker information 13 indicative of a number of loudspeakers and/or a spatial geometry of the loudspeakers. In some instances, the audio playback system 16 may obtain the loudspeaker information 13 using a reference microphone and driving the loudspeakers in such a manner as to dynamically determine the loudspeaker information 13. In other instances, or in conjunction with the dynamic determination of the loudspeaker information 13, the audio playback system 16 may prompt a user to interface with the audio playback system 16 and input the loudspeaker information 13.

The audio playback system 16 may select one of the audio renderers 22 based on the loudspeaker information 13. In some instances, the audio playback system 16 may, when none of the audio renderers 22 are within some threshold similarity measure (in terms of the loudspeaker geometry) to the loudspeaker geometry specified in the loudspeaker information 13, generate the one of audio renderers 22 based on the loudspeaker information 13. The audio playback system 16 may, in some instances, generate one of the audio renderers 22 based on the loudspeaker information 13 without first attempting to select an existing one of the audio renderers 22.

When outputting the speaker feeds 25 to headphones, the audio playback system 16 may utilize one of the renderers 22 that provides for binaural rendering using head-related transfer functions (HRTF) or other functions capable of rendering to left and right speaker feeds 25 for headphone speaker playback. The terms “speakers” or “transducer” may generally refer to any speaker, including loudspeakers, headphone speakers, etc. One or more speakers may then playback the rendered speaker feeds 25.

Although described as rendering the speaker feeds 25 from the HOA audio data 11′, reference to rendering of the speaker feeds 25 may refer to other types of rendering, such as rendering incorporated directly into the decoding of the HOA audio data 15 from the bitstream 21. An example of the alternative rendering can be found in Annex G of the MPEG-H 3D audio coding standard, where rendering occurs during the predominant signal formulation and the background signal formation prior to composition of the soundfield. As such, reference to rendering of the HOA audio data 15 should be understood to refer to both rendering of the actual HOA audio data 15 or decompositions or representations thereof of the HOA audio data 15 (such as the above noted predominant audio signal, the ambient HOA coefficients, and/or the vector-based signal—which may also be referred to as a V-vector).

As described above, the content consumer device 14 may represent a VR device in which a human wearable display is mounted in front of the eyes of the user operating the VR device. FIG. 3 is a diagram illustrating an example of a VR device 400 worn by a user 402. The VR device 400 is coupled to, or otherwise includes, headphones 404, which may reproduce a soundfield represented by the HOA audio data 11′ (which is another way to refer to HOA coefficients 11′) through playback of the speaker feeds 25. The speaker feeds 25 may represent an analog or digital signal capable of causing a membrane within the transducers of headphones 404 to vibrate at various frequencies, where such process is commonly referred to as driving the headphones 404.

Video, audio, and other sensory data may play important roles in the VR experience. To participate in a VR experience, the user 402 may wear the VR device 400 (which may also be referred to as a VR headset 400) or other wearable electronic device. The VR client device (such as the VR headset 400) may track head movement of the user 402, and adapt the video data shown via the VR headset 400 to account for the head movements, providing an immersive experience in which the user 402 may experience a virtual world shown in the video data in visual three dimensions.

While VR (and other forms of AR and/or MR) may allow the user 402 to reside in the virtual world visually, often the VR headset 400 may lack the capability to place the user in the virtual world audibly. In other words, the VR system (which may include a computer responsible for rendering the video data and audio data—that is not shown in the example of FIG. 3 for ease of illustration purposes, and the VR headset 400) may be unable to support full three dimension immersion audibly.

The audio aspects of VR have been classified into three separate categories of immersion. The first category provides the lowest level of immersion, and is referred to as three degrees of freedom (3DOF). 3DOF refers to audio rendering that accounts for movement of the head in the three degrees of freedom (yaw, pitch, and roll), thereby allowing the user to freely look around in any direction. 3DOF, however, cannot account for translational head movements in which the head is not centered on the optical and acoustical center of the soundfield.

The second category, referred to 3DOF plus (3DOF+), provides for the three degrees of freedom (yaw, pitch, and roll) in addition to limited spatial translational movements due to the head movements away from the optical center and acoustical center within the soundfield. 3DOF+ may provide support for perceptual effects such as motion parallax, which may strengthen the sense of immersion.

The third category, referred to as six degrees of freedom (6DOF), renders audio data in a manner that accounts for the three degrees of freedom in term of head movements (yaw, pitch, and roll) but also accounts for translation of the user in space (x, y, and z translations). The spatial translations may be induced by sensors tracking the location of the user in the physical world or by way of an input controller.

3DOF rendering is the current state of the art for VR. As such, the audio aspects of VR are less immersive than the video aspects, thereby potentially reducing the overall immersion experienced by the user.

In accordance with the techniques described in this disclosure, various ways by which to adjust higher order ambisonic (HOA) audio data may allow for 3DOF+ audio rendering. As noted above, 3DOF+ rendering provides a more immersive listening experience by rendering HOA audio data in a manner that accounts for both the three degrees of freedom in term of head movements (yaw, pitch, and roll) and limited translational movements (in a spatial two dimensional coordinate system—x, y—or a spatial three dimensional coordinate system—x, y, z) due to head movements not being centered on the optical and acoustical center.

In operation, the audio playback system 16 may first obtain head tracking information 17. The head tracking information 17 may include a translational distance representative of a translational head movement of a user interfacing with the content consumer device 14, a rotation indication indicative of a rotational head movement of the user interface with the content consumer device 14, or both the translation head movement and the rotation indication. The audio playback system 16 may obtain the head tracking information 17 in a variety of different ways. As shown in the example of FIG. 2A, content consumer device 14 interfaces with a tracking device 306. The tracking device 306 may represent any combination of a microelectromechanical system (MEMS) for sensing and video display, a camera or other visual sensor, or any other type of sensor capable of providing information in support of head and/or body tracking.

In one example, the tracking device 306 may represent the MEMS for sensing and video display similar to those used in cellular phones, such as so-call “smart phones.” The audio playback device 16 may obtain the head tracking information 17 using motion sensors included in the MEMS of the tracking device 306 that sense the translational head movement. More information regarding MEMS for sensing and video display being used to perform head tracking can be found in a paper by LaValle, et. al., entitled “Head Tracking for the Oculus Rift,” accessed on Aug. 17, 2017 at a URL of msl.cs.illinois.edu/˜lavalle/papers/LavYerKatAnt14.pdf.

In another example, the audio playback system 16 may interface with the tracking device 306, which may represent a camera (including infrared cameras) or other visual sensors, to identify the head tracking information 17. The audio playback system 16 may perform image analysis with respect to images captured by the tracking device 306. More information regarding head and body tracking using a camera and various other sensors can be found in a paper by Jesper Tingvall, entitled “Interior Design and Navigation in Virtual Reality,” dated Nov. 1, 2015.

While shown as being separate from the content consumer device 14, the tracking device 306 may be integrated into the content consumer device 14. In other words, the content consumer device 14 may include the tracking device 306, such as when the tracking device 306 represents the MEMS, which is a small semiconductor chip capable of being integrated in the content consumer device 14.

After determining the head tracking information 17, the audio playback system 16 may adapt, based on the head tracking information 17, the HOA audio data 15 to provide three degrees of freedom plus (3DOF+) effects that adapt the soundfield represented by the HOA audio data 15 to account for the translational head movement, the rotational head movement, or both the translational head movement and the rotational head movement.

To adapt the HOA audio data 15 in one example, audio playback system 16 determines an effect matrix 26. The effect matrix 26 may be similar to a preliminary effect matrix discussed in the MPEG-H 3D Audio Coding Standard used for loudness compensation and/or screen adaptation.

However, in performing loudness compensation and/or screen adaptation using the preliminary effects matrix, the audio playback system 16 does not adapt the preliminary effect matrix based on any translational movements of the user 402. In accordance with the techniques described herein, the audio playback system 16 may determine the effects matrix 26 based on the translational distance of the head tracking information 17 as discussed in more detail below.

While described in this disclosure as determining the effects matrix 26 based on the translation distance of the head tracking information 17, the audio playback system 16 may determine the effects matrix 26 based on the rotational indication of the head tracking information 17, or based on both the translational distance and the rotational indication of the head tracking information 17. In other words, the 3DOF+ effects incorporate the rotational aspects of 3DOF and further account for translational head movements. In this respect, the audio playback system 16 may obtain a rotation indication indicative of a rotational head movement of the user interfacing with the device, and based on the translational head distance and the rotation indication, the higher order ambisonic audio data to provide the three degrees of freedom plus effects that adapt the soundfield to account for the translational head movement and the rotational head movement.

Although the techniques may be performed with respect to the rotational indication, the techniques are described below with respect to the translational distance. As such, the head tracking information 17 is referred to below as the translational distance 17 for ease of explanation.

After generating the effect matrix 26, the audio playback system 16 may apply the effect matrix 26 to the selected one of audio renderers 22 (which may in the context of the VR device 400 with integrated headphones 404 refer to what is denoted herein as binaural renderer 22). The audio playback system 16 may generate an updated binaural renderer 22 through application of the effect matrix 26 to the binaural renderer 22. The audio playback system 16 may next apply the updated binaural renderer 22 to the HOA audio data 15 to both adapt, based on the translational distance 17, the HOA audio data 15 to provide the 3DOF+ effects, and generate speaker feeds 25 based on the adapted HOA audio data 15.

In this respect, the audio playback system 16 may perform various aspects of the techniques described in this disclosure to provide 3DOF+ rendering, resulting in more immersion compared to 3DOF rendering. The increased immersion relative to 3DOF+ may improve the overall immersion experienced by the user 402 and possibly provide a level of immersion that is equal to or exceeds the level of immersion provided by the video experience.

Although described with respect to a VR device as shown in the example of FIG. 3, the techniques may be performed by other types of wearable devices, including watches (such as so-called “smart watches”), glasses (such as so-called “smart glasses”), headphones (including wireless headphones coupled via a wireless connection, or smart headphones coupled via wired or wireless connection), and any other type of wearable device. As such, the techniques may be performed by any type of wearable device by which a user may interact with the wearable device while worn by the user.

FIG. 2B is a block diagram illustrating another example system 100 configured to perform various aspects of the techniques described in this disclosure. The system 100 is similar to the system 10 shown in FIG. 2A, except that the audio renderers 22 shown in FIG. 2A are replaced with a binaural renderer 102 capable of performing binaural rendering using one or more HRTFs or the other functions capable of rendering to left and right speaker feeds 103.

The audio playback system 16 may output the left and right speaker feeds 103 to headphones 104, which may represent another example of a wearable device and which may be coupled to additional wearable devices to facilitate reproduction of the soundfield, such as a watch, the VR headset noted above, smart glasses, smart clothing, smart rings, smart bracelets or any other types of smart jewelry (including smart necklaces), and the like. The headphones 104 may couple wirelessly or via wired connection to the additional wearable devices.

Additionally, the headphones 104 may couple to the audio playback system 16 via a wired connection (such as a standard 3.5 mm audio jack, a universal system bus (USB) connection, an optical audio jack, or other forms of wired connection) or wirelessly (such as by way of a Bluetooth™ connection, a wireless network connection, and the like). The headphones 104 may recreate, based on the left and right speaker feeds 103, the soundfield represented by the HOA coefficients 11. The headphones 104 may include a left headphone speaker and a right headphone speaker which are powered (or, in other words, driven) by the corresponding left and right speaker feeds 103.

FIG. 4 is a block diagram illustrating in more detail the audio playback system shown in FIGS. 2A and 2B in performing various aspects of the effect techniques described in this disclosure. As shown in the example of FIG. 4, audio playback system 16 includes an effects unit 510 and a rendering unit 512 in addition to the above described audio decoding device 24. The effects unit 510 represents a unit configured to obtain the effects matrix 26 (shown as “EM 26” in the example of FIG. 4) described above. The rendering unit 512 represents a unit configured to determine and/or apply one or more of the audio renderers 22 (shown as “ARs 22” in the example of FIG. 4) described above.

The audio decoding device 24 may, as noted above, represent a unit configured to decode bitstream 21 in accordance with the MPEG-H 3D Audio Coding Standard. The audio decoding device 24 may include a bitstream extraction unit 500, an inverse gain control and reassignment unit 502, a predominant sound synthesis unit 504, an ambient synthesis unit 506, and a composition unit 508. More information concerning each of the foregoing units 500-508 can be found in the MPEG-H 3D Audio Coding Standard.

While described in detail in the MPEG-H 3D Audio Coding Standard, a brief description of each of the units 500-508 is provided below. The bitstream extraction unit 500 may represent a unit configured to extract decompositions of the HOA coefficients 11, along with other syntax elements or data required to compose a representation of the soundfield defined by the HOA coefficients 11. The bitstream extraction unit 500 may identify one or more transport channels 501 in the bitstream 11, each of which may specify either an ambient audio signal (which may refer to one or more ambient HOA coefficients 11) or a predominant audio signal (which may refer to a multiplication of a U vector by an S vector decomposed from the HOA coefficients 11 through application of a linear invertible transform, such as a singular value decomposition, an eigenvalue decomposition, a KLT, etc.). The bitstream extraction unit 500 may extract the transport channels 501 and output the transport channels 501 to the inverse gain control and reassignment unit 502.

Although not shown in the example of FIG. 4 for ease of illustration purposes, the audio decoding device 24 may include a psychoacoustic audio decoder that performs psychoacoustic audio decoding (e.g., advanced audio coding—AAC) with respect to the transport channels 501. Moreover, the audio decoding device 24 may include further units that perform various other operations not shown in the example of FIG. 4, such as fading between transport channels 501, and the like.

The bitstream extraction unit 500 may further extract side information 521 defining syntax elements and other data for performing gain control and assignment. The bitstream extraction unit 500 may output the side information 521 to inverse gain control and reassignment unit 502.

The bitstream extraction unit 500 may also extract side information 523 defining syntax elements and other data for performing predominant sound synthesis (including, a vector defining spatial characteristics—such as a width, direction, and/or shape—of a corresponding predominant audio signal defined in the transport channels 501). Additionally, the bitstream extraction unit 500 may extract side information 525 defining syntax elements and other data for performing ambient synthesis. The bitstream extraction unit 500 outputs the side information 523 to the predominant sound synthesis unit 504, and the side information 525 to the ambient synthesis unit 506.

The inverse gain control and reassignment unit 502 may represent a unit configured to perform, based on the side information 521, inverse gain control and reassignment with respect to the transport channels 501. The inverse gain control and reassignment unit 502 may determine, based on the side information 521, gain control information and apply the gain control information to each of the transport channels 501 to invert gain control applied at the audio encoding device implemented by the soundfield representation generation 302 in an effort to reduce dynamic range of the transport channels 501. The inverse gain control and reassignment unit 502 may next, based on the side information 523, determine whether each of the transport channels 501 specifies a predominant audio signal 503 or an ambient audio signal 505. The inverse gain control and reassignment unit 502 may output the predominant audio signals 503 to the predominant sound synthesis unit 504 and the ambient audio signals 505 to the ambient synthesis unit 506.

The predominant sound synthesis unit 504 may represent a unit configured to synthesize, based on the side information 523, predominant audio components of the soundfield represented by the HOA coefficients 11. The predominant sound synthesis unit 504 may multiply each of the predominant audio signals 503 by a corresponding spatial vector (which may also be referred to as a “vector-based signal”) specified in the side information 523. The predominant sound synthesis unit 504 output, to composition unit 508, the result of the multiplication as predominant sound representation 507.

The ambient synthesis unit 506 may represent a unit configured to synthesize, based on the side information 525, ambient components of the soundfield represented by the HOA coefficients 11. The ambient synthesis unit 506 output, to composition unit 508, the result of the synthesis as ambient HOA coefficients 509.

The composition unit 508 may represent a unit configured to compose, based on predominant sound representation 507 and the ambient HOA coefficients 509, the HOA audio data 15. The composition unit 508 may, in some examples, add the predominant sound representation 507 (which may define predominant HOA coefficients describing a predominant sound of the soundfield originally represented by the HOA coefficients 11) to the ambient HOA coefficients 509 to obtain the HOA audio data 15. The composition unit 508 may output the HOA audio data 15 to the effects unit 510.

The effects unit 510 may represent a unit configured to perform various aspects of the effects techniques described in this disclosure to generate the EM 26 based on the translational distance 17, or as described in more detail below, the translational distance 17 and a depth map 509. The effects unit 510 may apply EM 26 to the HOA audio data 15 to obtain adapted HOA audio data 511. The adapted HOA audio data 511 may be adapted to provide the three degrees of freedom plus effects that accounts, in the soundfield, for the translational head movement indicated by the translational distance 17. The effects unit 510 may output the adapted HOA audio data 511 to rendering unit 512.

The rendering unit 512 may represent a unit configured to apply one or more of ARs 22 to adapted HOA audio data 511, and thereby obtain the speaker feeds 25. The rendering unit 512 may output the speaker feeds 25 to the headphones 404 shown in the example of FIG. 3.

Although described as separate units 510 and 512, the effects unit 510 may be incorporated within rendering unit 512, where the EM 26 is multiplied by the selected one of ARs 22 in the manner described below in more detail. The multiplication of the EM 26 by the selected one of ARs 22 may result in an updated AR (which may be denoted as “updated AR 22”). The rendering unit 512 may then apply the updated AR 22 to the HOA audio data 15 to both adapt the HOA audio data 15 to provide the 3DOF+ effect that accounts for the translational distance 17 and render the speaker feeds 25.

FIG. 5 is a diagram illustration in more detail how the effects unit shown in the example of FIG. 4 obtains the effects matrix in accordance with various aspects of the techniques described in this disclosure. As shown in the example of FIG. 5, the user 402 initially resides in the middle of recreated soundfield 600, as shown at the left of FIG. 5 denoted “INITIAL USER LOCATION.” The recreated soundfield 600, while shown as a circle, is modeled as a sphere surrounding the user 402 at a reference distance 602. In some examples, the user 402 may input the reference distance 602 in configuring VR device 14 for playback of the audio data. In other examples, the reference distance 602 is static, or defined as a syntax element of the bitstream 21. When defined using the syntax element, the reference distance 602 may be static (such as sent a single time and therefore static for the duration of the experience) or dynamic (such as sent multiple times during the experience, e.g., per audio frame or per some periodic or non-periodic number of audio frames).

The effects unit 510 may receive the reference distance 602 and determine anchor points 604 positioned at the reference distance 602 from the head of the user 402 prior the translational head movement 606. The anchor points 604 are shown in the example of FIG. 5 as “X” marks. The effects unit 510 may determine the anchor points 604 as a plurality of uniformly distributed anchor points on a surface of the spherical soundfield 600 having a radius equal to the reference distance 602.

The anchor points 604 may represent points of reference by which to determine translational head movement 606. The anchor points 604 may, in other words, represent reference points distributed about the spherical soundfield 600 by which the translational head movement 606 may be determined so as to adapt the soundfield. The anchor points 604 should not be confused with anchor points or key points as understood in visual image search algorithms. Again, the anchor points 604 may denote reference points at the reference distance from the head of user 402 used for determining the translational head movement 606 relative to each of the anchor points 604. The extent of the translational head movement 606 relative to each of the anchor points 604 may impact rendering with respect to the portion of the soundfield in which the respective one of the anchor points 604 resides. As such, the anchor points 604 may also represent soundfield sampling points by which to determine translational head movement 606 and adapt, based on the relative translational head movement 606, rendering of the soundfield.

In any event, the user 402 may then perform the translational head movement 606, moving, as shown in the example of FIG. 5 under the heading “USER LOCATION AFTER TRANSLATIONAL MOVEMENT,” the head the translational distance 17 to the right. The effects unit 510 may determine, after the translational head movement 606, an updated distance 608 relative to each of the plurality of anchor points 604. Although only a single updated distance 608 is shown in the example of FIG. 5, the effects unit 510 may determine an updated distance 608 relative to each of the anchor points 604. The effects unit 510 may next determine, based on each of the updated distances 608, the EM 26.

The effects unit 510 may compute a distant-dependent loudness adjustment (in the form of the EM 26) for each translated anchor point. The computation for each reference point may be denoted as g_(|), where the original reference distance 602 is denoted as dist_(ref) and the updated distance 608 may be denoted as dist_(new,|). For each of the anchor points 604, the effects unit 510 may compute g_(|) using the equation

${\mathcal{g}}_{❘} = {\left( \frac{{dist}_{ref}}{{dist}_{{new},❘}} \right)^{distPow}.}$ The distPow parameter may control the effect strength, which may be input by the user 402 to control the magnitude of the effect strength. While described as being a variable subject to control by the user 402, the distPow parameter may also be specified by the content creator either dynamically or statically.

Mathematically, the soundfield 600 surrounding the user 402 may be represented as M equidistant anchor points 604 (which may also be referred to as “spatial points 604”) on a sphere with a center located at the head of the user 402. The variable ‘M’ is typically selected such that M is greater than or equal to (N+1)², where N denotes the greatest order associated with the HOA audio data 15.

The M equidistant spatial points 604 result in M spatial directions extending from the head of the user 402 to each of the M equidistant spatial points 604. The M spatial directions may be represented by

_(m). The effects unit 510 may obtain the EM 26 that is applied to the rendering matrix based on the M spatial directions,

_(m). In one example, the effects unit 510 obtains EM 26 computed from HOA coefficients associated with each of the M spatial directions. The effects unit 510 may then perform loudness compensation for each of spatial direction l=1 . . . M, which is applied to the EM 26 to generate the compensated EM 26. While described as being M equidistant spatial point 604, the points 604 may also be non-equidistant or, in other words, distributed about the sphere in a non-uniform manner.

In terms of the variables used by the MPEG-H 3D Audio Coding Standard, Annex F.1.5 of the “DIS” version, when discussing, as one example, loudness compensation, the effects unit 510 may compute EM 26 from HOA coefficients associated with the M spatial directions as follows: {tilde over (F)}=(Ψ^((O,M)) ^(T) )†(Ψ_(m) ^((O,M)) ^(T) )

-   -   with Ψ^((0,M)) ^(T) :=[S₁ ^(O) S₂ ^(O) . . . S_(M) ^(O)] ∈         ^(O×M)         The “†” symbol may denote the pseudo-inverse matrix operation.

The effect unit 510 may then perform the loudness compensation for each spatial direction l=1 . . . M, which is applied for the matrix F according to the following:

${A(l)} = {\sqrt{\frac{\left( {RS}_{m_{l}}^{O} \right)^{T}\left( {RS}_{m_{l}}^{O} \right)}{\left( {R\overset{\sim}{F}S_{l}^{U}} \right)^{T}\left( {R\overset{\sim}{F}S_{l}^{U}} \right)}}*{\mathcal{g}}_{❘}}$ where  F = (Ψ^((O, M)^(T)))  †  diag(A)  (Ψ_(m)^((O, M)^(T))). The effect unit 510 may then multiple the selected one of AR 22, denoted below by the variable “R” by the EM 26, denoted above and below by the variable “F” to generate the updated AR 22 discussed above and denoted as follows by the variable “D.” D=RF

The foregoing may, when distance-dependent loudness adjustment is disabled, mathematically represent the distance-independent loudness adjustment by removal of the multiplication by g_(|), resulting in the following:

${A(l)} = \sqrt{\frac{\left( {RS}_{m_{l}}^{O} \right)^{T}\left( {RS}_{m_{l}}^{O} \right)}{\left( {R\overset{\sim}{F}S_{l}^{U}} \right)^{T}\left( {R\overset{\sim}{F}S_{l}^{U}} \right)}}$ In all other respects, the mathematic representation is unchanged when distance-independent loudness adjustment is enabled (or, in other words, when distance-dependent loudness adjustment is disabled).

In this way, the effects unit 510 may provide the EM 26 to rendering unit 512, which multiplies the audio renderer 22 that converts the HOA audio data 15 from the spherical harmonic domain to the spatial domain speaker signals 25 (which in this case may be a binaural render that renders the HOA audio data to binaural audio headphone speaker signals) by the compensated EM 26 to create an adapted spatial rendering matrix (which is referred to herein as the “updated AR 22”) capable of accounting for both the three degrees of freedom and the translation head movement 606.

In some instances, the effects unit 510 may determine multiple EMs 26. For example, the effects unit 510 may determine a first EM 26 for a first frequency range, a second EM 26 for a second frequency range, etc. The frequency ranges of the first EM 26 and the second EM 26 may overlap, or may not overlap (or, in other words, may be distinct from one another). As such, the techniques described in this disclosure should not be limited to the single EM 26, but should include application of multiple EMs 26, including, but not limited to, the example multiple frequency dependent EMs 26.

As discussed above, the effects unit 510 may also determine EM 26 based on translational distance 17 and the depth map 509. The bitstream 21 may include video data corresponding to the HOA audio data 16, where such video data is synchronized with the HOA audio data 16 (using, e.g., frame synchronization information). Although not shown in the example of FIGS. 2-4, the client consumer device 14 may include a video playback system that decodes the corresponding bitstream providing the video data, which may include depth maps, such as the depth map 509. The depth map 509 provides a gray scale representation of the 360 degree virtual reality scene, where black represents a very far distance, and white represents a near distance with the various shades of gray indicated intermediate distances between black and white.

The video decoding device of the video playback system may utilize the depth map 509 to formulate a view for either the left eye or the right eye from the respective right eye view or left eye view specified in the video bitstream. The video decoding device may alter the amount of lateral distance between the right eye view and the left eye view based on the depth map, scaling the lateral distance smaller based on the darker the shade of grey. As such, near objects denoted in white or light shades of gray in the depth map 509 may have a larger lateral distance between the left and right eye views, while far objects denoted in black or darker shades of gray in the depth map 509 may have a smaller lateral distance between the left and right eye view (thereby more closing resembling a far off point).

The effects unit 510 may utilize the depth information provided by the depth map 509 to adapt the location of the anchor points 604 relative to the head of the user 402. That is, the effects unit 510 may map the anchor points 604 to the depth map 509, and utilize the depth information of the depth map 509 at the mapped locations within the depth map 509 to identify a more accurate reference distance 602 for each of the anchor points 604. FIG. 6 is a diagram illustrating the depth map shown in FIG. 4 having been updated to reflect the mapping of the anchor points to the depth map in accordance with various aspects of the techniques described in this disclosure.

In this respect, instead of assuming a single reference distance 602, the effects unit 510 may utilize the depth map 509 to estimate individual references distances 602 for each of the anchor points 604. As such, the effects unit 510 may determine the updated distance 608 relative to each of the individually determined reference distances 602 of the anchor points 604.

While described as performed with respect to a gray-scale depth map 509, the techniques may be performed with respect to other types of information providing depth information, such as a color image, color or gray-scale stereo images, infrared camera images, etc. The techniques may, in other words, be performed with respect to any type of information providing depth information of a scene associated with the corresponding HOA audio data 15.

FIG. 7 is a diagram illustrating an example of a wearable device 800 that may operate in accordance with various aspect of the techniques described in this disclosure. In various examples, the wearable device 800 may represent a VR headset (such as the VR headset 400 described above), an AR headset, an MR headset, or an extended reality (XR) headset. Augmented Reality “AR” may refer to computer rendered image or data that is overlaid over the real world where the user is actually located. Mixed Reality “MR” may refer to computer rendered image or data that is world locked to a particular location in the real world, or may refer to a variant on VR in which part computer rendered 3D elements and part photographed real elements are combined into an immersive experience that simulates the user's physical presence in the environment. Extended Reality “XR” may refer to a catchall term for VR, AR, and MR. More information regarding terminology for XR can be found in a document by Jason Peterson, entitled “Virtual Reality, Augmented Reality, and Mixed Reality Definitions,” and dated Jul. 7, 2017.

The wearable device 800 may represent other types of devices, such as a watch (including so-called “smart watches”), glasses (including so-called “smart glasses”), headphones (including so-called “wireless headphones” and “smart headphones”), smart clothing, smart jewelry, and the like. Whether representative of a VR device, a watch, glasses, and/or headphones, the wearable device 800 may communicate with the computing device supporting the wearable device 800 via a wired connection or a wireless connection.

In some instances, the computing device supporting the wearable device 800 may be integrated within the wearable device 800 and as such, the wearable device 800 may be considered as the same device as the computing device supporting the wearable device 800. In other instances, the wearable device 800 may communicate with a separate computing device that may support the wearable device 800. In this respect, the term “supporting” should not be understood to require a separate dedicated device but that one or more processors configured to perform various aspects of the techniques described in this disclosure may be integrated within the wearable device 800 or integrated within a computing device separate from the wearable device 800.

For example, when the wearable device 800 represents the VR device 400, a separate dedicated computing device (such as a personal computer including the one or more processors) may render the audio and visual content, while the wearable device 800 may determine the translational head movement upon which the dedicated computing device may render, based on the translational head movement, the audio content (as the speaker feeds) in accordance with various aspects of the techniques described in this disclosure. As another example, when the wearable device 800 represents smart glasses, the wearable device 800 may include the one or more processors that both determine the translational head movement (by interfacing within one or more sensors of the wearable device 800) and render, based on the determined translational head movement, the speaker feeds.

As shown, the wearable device 800 includes a rear camera, one or more directional speakers, one or more tracking and/or recording cameras, and one or more light-emitting diode (LED) lights. In some examples, the LED light(s) may be referred to as “ultra bright” LED light(s). In addition, the wearable device 800 includes one or more eye-tracking cameras, high sensitivity audio microphones, and optics/projection hardware. The optics/projection hardware of the wearable device 800 may include durable semi-transparent display technology and hardware.

The wearable device 800 also includes connectivity hardware, which may represent one or more network interfaces that support multimode connectivity, such as 4G communications, 5G communications, etc. The wearable device 800 also includes ambient light sensors, and bone conduction transducers. In some instances, the wearable device 800 may also include one or more passive and/or active cameras with fisheye lenses and/or telephoto lenses. Various devices of this disclosure, such as the content consumer device 14 of FIG. 2A may use the steering angle of the wearable device 800 to select an audio representation of a soundfield (e.g., one of MOA representations) to output via the directional speaker(s)—headphones 404—of the wearable device 800, in accordance with various techniques of this disclosure. It will be appreciated that the wearable device 800 may exhibit a variety of different form factors.

Furthermore, the tracking and recording cameras and other sensors may facilitate the determination of translational distance 606. Although not shown in the example of FIG. 7, wearable device 800 may include the above discussed MEMS or other types of sensors for detecting translational distance 606.

Although described with respect to particular examples of wearable devices, such as the VR device 400 discussed above with respect to the examples of FIG. 3 and other devices set forth in the examples of FIGS. 2A and 2B, a person of ordinary skill in the art would appreciate that descriptions related to FIGS. 2A-3 may apply to other examples of wearable devices. For example, other wearable devices, such as smart glasses, may include sensors by which to obtain translational head movements. As another example, other wearable devices, such as a smart watch, may include sensors by which to obtain translational movements. As such, the techniques described in this disclosure should not be limited to a particular type of wearable device, but any wearable device may be configured to perform the techniques described in this disclosure.

FIGS. 8A and 8B are diagrams illustrating example systems that may perform various aspects of the techniques described in this disclosure. FIG. 8A illustrates an example in which the source device 12 further includes a camera 200. The camera 200 may be configured to capture video data, and provide the captured raw video data to the content capture device 300. The content capture device 300 may provide the video data to another component of the source device 12, for further processing into viewport-divided portions.

In the example of FIG. 8A, the content consumer device 14 also includes the wearable device 800. It will be understood that, in various implementations, the wearable device 800 may be included in, or externally coupled to, the content consumer device 14. As discussed above with respect to FIG. 7, the wearable device 800 includes display hardware and speaker hardware for outputting video data (e.g., as associated with various viewports) and for rendering audio data.

FIG. 8B illustrates an example similar that illustrated by FIG. 8A, except that the audio renderers 22 shown in FIG. 8A are replaced with a binaural renderer 102 capable of performing binaural rendering using one or more HRTFs or the other functions capable of rendering to left and right speaker feeds 103. The audio playback system 16 may output the left and right speaker feeds 103 to headphones 104.

The headphones 104 may couple to the audio playback system 16 via a wired connection (such as a standard 3.5 mm audio jack, a universal system bus (USB) connection, an optical audio jack, or other forms of wired connection) or wirelessly (such as by way of a Bluetooth™ connection, a wireless network connection, and the like). The headphones 104 may recreate, based on the left and right speaker feeds 103, the soundfield represented by the HOA coefficients 11. The headphones 104 may include a left headphone speaker and a right headphone speaker which are powered (or, in other words, driven) by the corresponding left and right speaker feeds 103.

FIG. 9 is a flowchart illustrating an example process 700 that the audio playback device may perform in accordance with various aspects of this disclosure. Initially, the audio playback device 16 of FIG. 2A may, as described above, obtain the translational distance 17 representative of the translational head movement 606 of the user interfacing with the device 14 shown in the example of FIG. 5 (702).

After receiving the translational distance 17 and in the manner described above, the audio playback device 16 may adapt, based on the translational distance 17, the HOA audio data 15 to provide the three degree of freedom plus (3DOF+) effects that adapt the soundfield 600 to account for the translational head movement 306 (704). The audio playback device 16 may then generate the speaker feeds 25, again as described above, based on the adapted HOA audio data 511 (706). The audio playback device 16 may next output the speaker feeds 25 for playback by the headphones 404 (708).

As noted above, when outputting the loudspeaker feeds 25 to headphones, the audio playback system 16 may utilize one of the renderers 22 that provides for binaural rendering using head-related transfer functions or other functions. The terms “speakers” or “transducer” may generally refer to any speaker, including loudspeakers, headphone speakers, etc. One or more speakers may then playback the rendered speaker feeds 25.

It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

In some examples, the VR device (or the streaming device) may communicate, using a network interface coupled to a memory of the VR/streaming device, exchange messages to an external device, where the exchange messages are associated with the multiple available representations of the soundfield. In some examples, the VR device may receive, using an antenna coupled to the network interface, wireless signals including data packets, audio packets, video pacts, or transport protocol data associated with the multiple available representations of the soundfield. In some examples, one or more microphone arrays may capture the soundfield.

In some examples, the multiple available representations of the soundfield stored to the memory device may include a plurality of object-based representations of the soundfield, higher order ambisonic representations of the soundfield, mixed order ambisonic representations of the soundfield, a combination of object-based representations of the soundfield with higher order ambisonic representations of the soundfield, a combination of object-based representations of the soundfield with mixed order ambisonic representations of the soundfield, or a combination of mixed order representations of the soundfield with higher order ambisonic representations of the soundfield.

In some examples, one or more of the soundfield representations of the multiple available representations of the soundfield may include at least one high-resolution region and at least one lower-resolution region, and wherein the selected presentation based on the steering angle provides a greater spatial precision with respect to the at least one high-resolution region and a lesser spatial precision with respect to the lower-resolution region.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples are within the scope of the following claims. 

What is claimed is:
 1. A device comprising: a memory configured to store higher order ambisonic audio data representative of a soundfield; and one or more processors coupled to the memory, and configured to: receive an original reference distance; determine reference points, wherein the reference points are anchor points, positioned at the original reference distance relative to the head of a user prior to a translational movement of the user interfacing with the device; obtain a translational distance representative of a translational head movement of a user interfacing with the device; determine, after the translational distance has been obtained, updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user; determine, prior to application of a renderer, based on each of the updated distances, an effects matrix; generate higher order ambisonic audio data, based on the effects matrix, to adapt the soundfield to account for the translational distance obtained; and generate speaker feeds based on the adapted generated higher order ambisonic audio data.
 2. The device of claim 1, wherein the translational distance representative of the translational head movement is defined in either a two-dimensional spatial coordinate space or a three-dimensional spatial coordinate space.
 3. The device of claim 1, wherein the one or more processors are further configured to multiply the effects matrix by a rendering matrix to obtain an updated rendering matrix, wherein the one or more processors are configured to apply the updated rendering matrix to the higher order ambisonic audio data to 1) provide one or more effects that adapt the soundfield to account for the translational distance and 2) generate the speaker feeds.
 4. The device of claim 1, wherein the plurality of anchor points are uniformly distributed on a surface of a sphere having a radius equal to the original reference distance.
 5. The device of claim 1, wherein three-dimensional video data including a depth map is associated with the higher order ambisonic audio data, and wherein the one or more processors are configured to determine the original reference distance of each of the anchor points based on the depth map prior to determining each of the updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user.
 6. The device of claim 1, wherein three-dimensional video data including a depth map is associated with the higher order ambisonic audio data, and wherein the one or more processors are configured to obtain, based on the depth map, the updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user.
 7. The device of claim 1, wherein the one or more processors are coupled to speakers of the device, wherein the device is a wearable device, wherein the one or more processors are configured to apply, the renderer, wherein the renderer is a binaural renderer to the adapted higher order ambisonic audio data to generate the speaker feeds, and wherein the one or more processors are further configured to output the speaker feeds to the speakers.
 8. The device of claim 7, wherein the wearable device is a watch, glasses, headphones, an augmented reality (AR) headset, a virtual reality (VR) headset, or an extended reality (XR) headset.
 9. The device of claim 1, wherein the one or more processors are-further configured to obtain a rotation indication indicative of a rotational head movement of the user interfacing with the device, and wherein the one or more processors are-configured to, based on the translational distance and the rotation indication, adapt the soundfield to account for the translational distance and the rotational indication.
 10. The device of claim 1, wherein the one or more processors are configured to obtain the translational distance using motion sensors that sense the translational head movement.
 11. The device of claim 1, wherein the one or more processors are configured to obtain the translational distance based on images captured by a camera coupled to the one or more processors.
 12. The device of claim 1, wherein the higher order ambisonic audio data comprises higher order ambisonic coefficients associated with spherical basis functions having an order of one or less, higher order ambisonic coefficients associated with spherical basis functions having a mixed order and suborder, or higher order ambisonic coefficients associated with spherical basis functions having an order greater than one.
 13. The device of claim 1, wherein the receive an original reference distance is configurable for playback of higher order ambisonic audio data, and, is based on a user input.
 14. The device of claim 1, wherein the original reference distance is static.
 15. The device of claim 1, wherein the original reference distance is dynamic.
 16. The device of claim 1, wherein the receive an original reference distance is received as a syntax element of a bitstream, to be decoded by a playback device.
 17. A method comprising: receiving an original reference distance; determining reference points, wherein the reference points are anchor points, positioned at the original reference distance relative to the head of a user prior to a translational movement of the user interfacing with a device; obtaining a translational distance representative of a translational head movement of the user interfacing with the device; determining, after the translational distance has been obtained, updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user; determining, prior to application of a renderer, based on each of the updated distances, an effects matrix; generating higher order ambisonic audio data, based on the effects matrix, to adapt a soundfield represented by the higher order ambisonic audio data to account for the translational distance obtained; and generating speaker feeds based on the generated higher order ambisonic audio data.
 18. The method of claim 17, wherein the translational distance representative of the translational head movement is defined in either a two-dimensional spatial coordinate space or a three dimensional spatial coordinate space.
 19. The method of claim 17, further comprising multiplying the effects matrix by a rendering matrix to obtain an updated rendering matrix, generating the speaker feeds comprises applying the updated rendering matrix to the higher order ambisonic audio data to 1) provide one or more effects that adapt the soundfield to account for the translational distance and 2) generate the speaker feeds.
 20. The method of claim 17, wherein the plurality of anchor points are uniformly distributed on a surface of a sphere having a radius equal to the original reference distance.
 21. The method of claim 17, wherein three-dimensional video data including a depth map is associated with the higher order ambisonic audio data, and wherein the determining the original reference distance of each of the anchor points is based on the depth map prior to determining each of the updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user.
 22. The method of claim 17, wherein three-dimensional video data including a depth map is associated with the higher order ambisonic audio data, and wherein obtaining the, updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user is based on the depth map.
 23. The method of claim 17, wherein generating the speaker feeds comprises applying, the renderer, wherein the renderer is a binaural renderer to the adapted higher order ambisonic audio data to generate the speaker feeds, and wherein the method further comprises outputting the speaker feeds to headphone speakers.
 24. The method of claim 17, further comprising obtaining a rotation indication indicative of a rotational head movement of the user interfacing with the device, and wherein based on the translational distance and the rotation indication, adapt the soundfield to account for the translational distance and the rotational indication.
 25. The method of claim 17, wherein obtaining the translational distance comprises obtaining the translational distance using motion sensors that sense the translational head movement.
 26. The method of claim 17, wherein obtaining the translational distance is based on images captured by a camera coupled to the device.
 27. The method of claim 17, wherein the method is performed by a virtual reality headset, an augmented reality headset, or a mixed reality headset.
 28. The method of claim 17, wherein the higher order ambisonic audio data comprises higher order ambisonic coefficients associated with spherical basis functions having an order of one or less, higher order ambisonic coefficients associated with spherical basis functions having a mixed order and suborder, or higher order ambisonic coefficients associated with spherical basis functions having an order greater than one.
 29. A device comprising: means for receiving an original reference distance; means for determining reference points, wherein the reference points are anchor points, positioned at the original reference distance relative to the head of a user prior to a translational movement of the user interfacing with the device; means for obtaining a translational distance representative of a translational head movement of a user interfacing with the device; means for determining, after the translational distance has been obtained, updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user; means for determining, prior to application of a renderer, based on each of the updated distances, an effects matrix; means for generating higher order ambisonic audio data, based on the effects matrix, to adapt a soundfield represented by the higher order ambisonic audio data to account for the translational distance obtained; and means for generating speaker feeds based on the means for generating higher order ambient audio data.
 30. A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to: receive an original reference distance; determine reference points, wherein the reference points are anchor points, positioned at the original reference distance relative to the head of a user prior to a translational movement of the user interfacing with the device; obtain a translational distance representative of a translational head movement of a user interfacing with a device; determine, after the translational distance has been obtained, updated distances between each of the anchor points, positioned at the original reference distance, and the head of the user; determine, prior to application of a renderer, based on each of the updated distances, an effects matrix; generate higher order ambisonic audio data, based on the effects matrix, to adapt the soundfield to account for the translational distance obtained; and generate speaker feeds based on the generated higher order ambisonic audio data. 